1. Field of the Invention
The present invention relates to an orthogonal frequency division multiplexing (OFDM) receiver system, and more particularly to an OFDM receiver system for performing demodulating operation after storing FFT-processed OFDM signals according to a predetermined rearrangement rule and extracting specific pilot signals.
2. Description of the Related Art
In an OFDM method, serially-inputted symbol streams are divided into unit blocks. The symbol streams of each unit block are converted into N number of parallel symbols. After the conversion, these symbols are multiplexed and added by using a plurality of subcarriers having different frequencies, respectively, according to Inverse Fast Fourier Transform (IFFT) algorithm and transmitted via the channel. That is, the N number of parallel symbols are defined as one unit block, and each subcarrier of the unit block has an orthogonal characteristic, which does not have an influence on subchannels. Consequently, in the OFDM method, the Inter-Symbol Interference (ISI) caused by multi-path fading can be reduced by increasing symbol period in proportion to the number of subchannels (N) while maintaining the same symbol transmission rate as that of a single carrier transmission method. Especially, a guard interval is inserted between the transmitted symbols to enhance the capability of the ISI reduction. As a result, a channel equalizer of simplified structure can be implemented.
In the above OFDM method, according to the Digital Video Broadcasting (DVB) standards, a transmission signal comprises frames, and each frame has a period of TF and 68 OFDM symbols. A superframe comprises four frames. Each symbol is formed by 6817 carriers in the case of an 8K mode and 1705 carriers in the case of a 2K mode (where K is the number of carriers), and has a symbol period of Ts.
In addition to the transmitted data, the OFDM transmission frame includes scattered pilot cells (SPC), continual pilot carriers (CPC), transmission parameter signaling pilots (TPS), etc. These pilot signals are used for frame synchronization, frequency synchronization, time synchronization, channel estimation, transmission mode identification or phase noise tracing. The pilot cells used as reference signals during demodulation are transmitted with a boosted power level, that is, about 1.4 times of the data level, and exist at specifically fixed carrier positions. Thus, in a receiver side, compensation of channel distortion generated during transmission and various kinds of synchronization can be performed using the carrier positions of the pilot cells and the information on the power level during transmission.
In general, an OFDM demodulation procedure includes an FFT step, a synchronizing step, an equalizing and deinterleaving step and a forward error correction (FEC) step. The synchronizing step is processed in the order of coarse time synchronization, coarse frequency synchronization, frame synchronization, fine frequency synchronization and fine time synchronization. Then, phase noise estimation and correction are performed and then symbol equalization is performed. Finally, the equalized symbols are demapped and deinterleaved.
However, conventional OFDM receiver systems require a considerable memory capacity for various kinds of synchronization, such as time synchronization, frequency synchronization or frame synchronization. Also, implementation of components for performing the same functions, for example, operators for complex number multiplication or pilot extraction, is overlapped, resulting in consumption of resources.
To solve the above problems, it is an object of the present invention to provide an OFDM receiver system having an optimal structure in view of resource utilization efficiency and chip area, by sharing common resources in a time-divisional manner by storing FFT-processed OFDM signals according to a predetermined rearrangement rule and extracting specific pilot signals in sequentially processed synchronization steps.
It is another object of the present invention to provide an OFDM receiver system which can reduce fabrication cost and architecture time and can obtain a reliable verification result.
To achieve the above objects, there is provided an orthogonal frequency division multiplexing (OFDM) receiver system comprising: a receiving section for receiving an OFDM signal, converting the same into a digital signal, and compensating a phase error and a frequency error of the digitally converted OFDM signal; a pilot signal decoding section for FFT-processing the output of the receiving section, and sequentially storing pilot signals and data separately according to a rearrangement rule; a synchronizing section for receiving the output of the pilot signal decoding section, performing coarse time synchronization, coarse frequency synchronization, frame synchronization, fine frequency synchronization and fine time synchronization, estimating a phase noise and correcting the same; an equalizing and deinterleaving section for performing a channel equalization algorithm on the output of the pilot signal decoding section using a reference pilot signal of the synchronizing section, restoring the equalized symbol into the original symbol, and rearranging the symbol in the order of the original symbol; and a controller for controlling the timing of data rearrangement in the pilot signal decoding section and feed-back controlling the receiving section according to the outputs of the respective synchronization results.